Centrifugal fan



Dee. i6

A Watts Input' Pre ent Efficiency Pressure in Inc/:e5 of Wer N WITNESSES:

c. J. FEcHl- IEIMER CENTRIEUGAL EAN Filed Nov. i0, 1922 2' sheets-sheet 'zooo INVENTOR CaPL J FechheiMeP.

ATTORNEY Patented Dec. 16, 1924.

UNITED STATES A 1,519,245` `PATENT oFFlcE.

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HOUSE ELECTBI VANIA.

` or PITTSBURGH, rnNnsYLvANI-A, nssmnon 'ro wasmaa` MANUr-Ac'runme confirman conronurron or rmmsvm CENTBIFUGAL FAN.

Application illed November 10, 1922. Seal No. 599,999.

' To all whom t may concern.:

' Be it known that I, CARL J. FECHHEIMER, a citizen of the United' States, and a resident of Pittsburgh, inthe county of Allegheny and St-ate of Pennsylvania, have invented a new and useful Improvement in Centrifugal Fans, of which the following is a specification.

My invention relates, in general, to centrifu al pumps and fans and has particular re ation to the impellers of centrifugal pumps or fans, designed for supplying relatively large volulnes of water or air at relatively low pressures while operating at high angular velocities.

In problems of Ventilating dynamo-electric machinery, and in many commercial problems ofventilating buildings and the like, `it is desirable to force relatively large volumes of air through ducts having rather small resistances, whereby the ressure head i of the air will be correspon ingly small. When` a direct-connected electric motor was used for `driving' afan designed along lines 25. with whichI was acquainted prior to the conception of my present invention, it was difficult to secure an eicient fan to deliver s uiiciently low pressures without reducing the speed of the impeller to such low values as to require a Amotor of undesirable proportions. A similar statement applies .to

- steam turbine drives and to certain other forms of direct motor drive. In many installations, the fan has been belt-driven by a high-speed motor; in others the fan selected for-"direct-connection is operated so low on its characteristic pressure-volume curve as to be ineiiicient and require a large motor and greater power consumption. Ac- 40 cording to my invention, I have evolved a highly eiiic'ient fan wherein the angular velocity is relatively high, even for large volumes and low ressures.

In all venti atin problems, moreover, it is extremely diilicu t to calculate, with even a rough approximation, the resistance to the flow of the air currents, and, hence, the required pressure head for a given rate of flow cannot be accurately predicted prior to the installation of the blower.

In centrifugal fans, such as were used prior to my present invention, the power input at an given speed increased very rapidly as t e volume of the air flow injing detailed description, when read in convlianges 12, one of determine the size of electric motor which would be necessary to drive the blower in actual practice. l Accordin to my invention, I have evolved a esign wherein the power input is approximately constant over a relatively wide range. y

Moreover, in many centrifugal fans, a large number of curved blades are employed, which make the fans more expensive. ne n of the advantages of my invention is that y the number of blades is small, and, in the preferred form, they are straight kinstead of curved.

Still another advantage of my invention is the fact that the fan operates with very little noise. 1

' The foregoing and other objects of my invention w1ll be apparent from the follownection with the accompanying drawing,

Figure 1 is a fragmentary longitudinal section of an impeller constructed-in accordance with my invention.

Fig. 2 is a fragmentary end view thereof.

Fig. 3 is a fragmentary end view showing a slight modification.

Fig. 4 is a diagrammatic view showing my invention with a volute collecting devlce.

Fig. 5 is a side elevational view, partly in section, showing my invention applied to a dyamo-electric machine to cool the same, an

Figs. 6, 7 and 8 are curve diagrams illustrating the variation of the Watts input, the eiiiciency and the pressure head, respectively, with respect to the volume of air per minute.`

Referring first to Figs. 1 and 2, my fan is shown as comprising a supporting disc 10 adapted to be rotated at al high velocity and carrying a plurality of flat blades 11,l l each of which is powded with two end 10o w 'ch is bolt/ed orY riveted tothe disc 10` and the other of which is bolted or riveted to a flanged ring 13 which serves to sup rt the outer ends of the blades. The anged` ring 13 is adapted to coo erate also with a stationary shroud, as indicated at 14 in Fig. 5, whereby a small clearance 16 is provided lfor reducing air leakage. As shown in Fig. 1, the rivets used for holding the blades in position are 110 counter-sunk, in order to the resistance to the ow of the air. The feature just mentioned is not essential but it is very desirable in order to reduce the internalpressure dropand to-improve the .eiiiciencyn As aresult of much experimentation and study, it has been found that the angle betwn the inner ends of the blades 11 and the.

tangent at that point should be approximately While some departure from the 25 value may be resorted to without seriously v affecting the operation, and while I do not care to be restricted to an exact angle, I have found that if an angle of about 25 is emi 3. spects,l it is also possible to employ blades ployed, together with other features which.

ile I have found that the straight or flat blade isthe more economical to manufacture and the more ldc'isirable in some rewhich may be curved, as indicated at 11a. in

l Fi 3.

e number vof blades is also important, as it has been found that, where the blades are so close together that each blade overf laps, or nearly overlaps, the adjacent blade,

such that a radiusintersecting the outer end of one blade will also intersect the inner end rof the next adjacent blade, the operating characteristics of the fan are not nearly sodesirable as if a much smaller number of blades is employed. In my tests, I have found that twelve isa very satisfactory number of blades to employ, as indicated in Fi s. 2, 3 'and`4, and that, if a number of bla es is chosen which is on the order of twelve blades, together with the other features of design, such as thel8 0% ratio of diameters andthe 25 entrance angle, a centrifu l fan will be produced havni improved characteristics for t remarka ly problems outlined above.

- in rigs. cio sus shown characteristic andthe dot-and-dash, curve C rformance curves taken without a collect- I ing device, such asa volute. In Fig. 6, the Aheavy curve A showsthepower-volume char eetenstic of a fan `twelve` straight had inclined a a A25 england with an 'ce 88% ratio of diametersg th'e-dotted curve B recents the similar characteristic curve o a fan e'mplo twelve straight'blades inclined at 25 wit a 67% ratio of diams-,- repre-4 sents vthe corresponding characteristic of a fan having12 curved blades as in le Ventilating 3. The corresponding eiciency and: pressure curves are shown in Figs. 7 and8, Afrom which it will be clear `that my invention achieves, in a very remarkable manner, the results outlined hereinabove. If the lfan is provided with a suitable collecting device, such as a volute, the power input is nearly the same, whereas the pressure and volumes are increased, thereby improvin the eiiiciencies, as has been determined y tests on my fan with various forms of collecting devices. Even with such increase in pressure, however, a relatively 'hi h angular velocity is still necessary, in or er to secure such pressures as are usually required in practice.A The eiciencies would also be improved by counter-sinking the rivet heads, the particular tests given having been made on afan with projecting rivet In Fig. 4, my invention is shown applied to a blower which is adapted to be driven by an independent electric motor, not shown, yand which comprises the impeller member shown -in Figs. 1 and 2 mounted in a volute v casin`17, 'as is customary in the art.

Inv ig. 5 the invention is shown a plied .to the rotor member of a d namo-e ectric machine 18, wherein the fan lades 11b are utilized'to force air within the generator end bell 19 inl a manner which will be obvious in view of the foregoing explanation.' In actual practice, the particular machine illustrated in Fig. 5 is provided with fourteen blades, as such slight de arturo in the number of blades does not a ect the performance appreciably. l

While I have illustrated my invention a number of specific forms which are at present preferred b me, and while I haveattempted to exp ain vthe same in accordance withiny present understanding of the o ration thereof, I desire it to be underst that the values stated in the foregoing descrip- 'tion are to be taken as illustrative only and that -slight modifications may be resor 0 to,'as .vvill'be vobvious to those skilled in the art, without departingfrom; the essential features of my invention, as outlined in the a pendedclaims. v

I as giaiilventioilil: f y A. 1. centri impe er or impelhng fluids, embodying a plurality of backwardly directed bla es each being .inchned rear `:wardlyv at an angle approximately twentyfivedegreesto atangent thereof. 2. A uidf' pelling device embodying aplurality of substantially dat bladeshaving entrance angles of'approximately twenty-five d with respect to thetangent.. 8. A; centrifugal impeller lfor impelling uids,embod ingeilurahtyjof backwardly. directedbles, D inclinedrear wardly at lan le ap proxiiiiiiitely.l tiventyfive degrees to a tangent thereof, none of said blades radiall overlappin another.

4. A Huid-impe ling centri gal device embodying a plurality of substantially AflatV blades having entrance angles of approximately twenty-five degrees with respect to the tangent, none of said blades radially overlapping another.

5. A iluid-impelling centrifugal device embodying` a plurality of blades having entrance angles'of approximately twenty-live degrees with respect to the tangent, said blades having a ratio of internal diameter to external diameter greater than 60%.

6. A fluid-impelling centrifugal device embodying a plurality of substantially fiat blades having entrance angles of approximately twenty-live degrees with' respect to the tangent, the ratio of the inner diameter to the outer diameter of said blades being upwards of eight-tenths.

7. In a fluid-impelling device, an impeller embodying a relatively small number of relativel shallow, fiat blades each inclined rearwar ly at an angle of approximately twent -fve degrees to a tangent thereof, where y a substantially constant power input is required to drive the device over -a relatively wide working range.

`8. In a iiuid-impelling devlce, an'impelle'r embodying a 'relatively small number of relativelyvshallow, Hat blades each inclined and adapted to operate at low hea irearwardlyv at an angle of approximately twenty-five degrees to a tangent thereof, and means for drivin said impeller at a relatively high rate o s eed.

9. In a fluid-im e ling device, animpeller embodyin a jrelatlvely small number of rela- .tivel shal ow, ilat blades, each inclined rearwar ly at an angle of approximately 'twentylive degrees to a tangent thereof.

10. A centrifugal fan for forcin` gases 'rearwardly inclined blades having ya ratio of internal diameter to external diameter of approximately eight-tenths, said blades having entrance angles of approximately twentyfive degrees with respect to the tangent,

'whereb a substantially constant power input is o rtained over a wide range of volumes of How.

In testimony whereof, I have "ereunto subscribed my name this 24th day of October 1922.

y CARLhJ. FEoHHEImR.

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